1. Field of the Invention
The present invention is based on a method for manufacturing a valve-seat body having a valve seat for a fuel injector and for manufacturing a fuel injector.
2. Background Information
German Application No. 40 37 952 already describes a fuel injector having a valve-seat body which, inter alia, has a guide bore and a valve seat. The guide bore serves for guiding an axially movable valve needle which is provided with a valve-closure member designed as a ball. This ball co-operates with the valve seat which tapers frustoconically in the downstream direction, forming a sealing-seat valve with it. In the guide bore located upstream of the valve seat, guide sections and fuel ducts alternate over the circumference of the guide bore. In the case of a conventional valve-seat body of this kind, both the guide sections and the valve seat are reworked upon reforming (massive forming, turning). In this context, the guide sections are machined separately from the machining of the valve seat in terms of time and tools by relatively inaccurate internal cylindrical grinding. In internal cylindrical grinding, an abrasive pencil is introduced into the guide bore and used for machining the guide sections in a rotational movement. The valve seat is also fine-machined by grinding, additional reworking by honing being necessary depending on the requirements. To achieve a high rotational accuracy combined with an optimum sealing behavior, several machining tools and sequential fine-machining steps are necessary.
Known from, for example, German Application No. 196 02 068, is a method for manufacturing rotationally symmetric valve-seat faces having a high surface finish at valves, in which method the valve seat is reworked as described above using a spherical tool body. In this context, the spherical tool body is designed with a diameter which is smaller than the cross-section of the guide opening in the valve-seat body to be machined so that only the immediate valve-seat face is fine-machined. The clearance of the guide opening must inevitably be greater than the diameter of the spherical tool since the tool could otherwise not immerse through the, in an axial direction, relatively long guide opening up the valve-seat face in the valve-seat body at all. Furthermore, there is such a great cutting volume for fine-machining in such a cylindrical guide opening that it is impossible to use a spherical tool body for the guide area.
Furthermore, German Patent Application No. 195 37 382 already describes a fuel injector which has a valve-seat body as well as a disk-shaped guide body lying upstream thereof. In this context, the guide body has an at least partially dome-shaped internal guide opening for a spherical valve member. The valve-seat body and the guide body are fine-machined, in each case, separately of each other at their internal openings to be made accurately. This is also carried out using different machining tools in different chucks.